The present invention relates to an object detection system. Such a system may be used, for example, as part of an adaptive cruise control in a motor vehicle. Such a control can regulate a previously set driving speed and/or a previously set distance from a vehicle in front or from objects in the direction of travel without intervention by the driver. This is done with appropriate regard for the environment around the motor vehicle and optionally additional parameters such as visibility and weather conditions. Such a control is known as an adaptive cruise control system (ACC system). The ACC system must be flexible enough to react appropriately to all driving situations, especially in view of today""s growing traffic density. This in turn requires an appropriate object detection sensor system to supply the measured data required for control purposes in all driving situations.
A plurality of different technical concepts/systems are available for object detection; some of these are described in greater detail below.
German Published Patent Application No. 43 30 476 discloses an optical radar system for a motor vehicle. This radar system contains essentially a light emitting unit for emitting light in the direction of a target object and a light receiving unit for receiving the light reflected by the target object. The light receiving unit contains a condenser lens, which is arranged to capture the reflected light, and a light-sensitive element arranged in an offset position relative to a focal point of the condenser lens by a preselected distance in an imaging space so it is exposed to light propagating from the condenser lens to ensure a narrower detection zone for a remote target object and a wider detection zone for a nearby target object. In other words, in order to ensure a narrower detection zone for a remote target object and a wider detection zone for a nearby target object, a first and second light-sensitive element are arranged in appropriate positions in an imaging space of a first and second condenser lens. Such an optical radar system based on light emission and light reception is also referred to below as a LIDAR (light detection and ranging) sensor.
German Published Patent Application No. 197 13 826 describes a radar device and a vehicle safety distance control system using this radar device. This radar device has a rotating polygonal mirror having a plurality of mirror surfaces inclined at different angles. A semiconductor laser diode and a collimator lens are arranged above the polygonal mirror. An infrared pulsed beam emitted by the laser diode is reflected by a reflective mirror arranged at an upper location in front of the polygonal mirror to reflect the pulsed beam downward obliquely toward the rotating polygonal mirror in such a way that the pulsed beam is reflected as a transmitted beam traveling toward a measurement zone in a forward direction. A light receiving device receives the transmitted beam returning from an object inside the measurement zone. Due to the use of a rotating polygonal mirror, two-dimensional scanning in the forward direction is possible, so that the pulsed beam can be swiveled horizontally due to the rotation of the polygonal mirror, and the pulsed beam can be swiveled vertically due to the faces of the polygonal mirror inclined at different angles. On the basis of the time between transmission of the pulsed beam and reception of the reflected beam, a calculation circuit determines a distance, an angle and a speed relative to a vehicle traveling in front that has been detected.
Such a radar device based on light is also referred to below as a LIDAR sensor.
German Published Patent Application No. 195 30 065 describes a monostatic FMCW radar sensor for a motor vehicle for detecting objects. In the case of this radar sensor, high frequency microwave beams (in the range of approx. 76 to 77 GHz) are sent out over antenna feeds designed for both sending and receiving a corresponding echo signal. The beams are concentrated by upright dielectric emitters located in the path of the beam and focused by a dielectric lens. Millimeter waves are generated by a Gunn oscillator driven by a stabilization network which contains a linearization network having a frequency regulator. Millimeter waves generated in this way are sent over conductors to parallel rat-race rings and from there are beamed over antenna feeds. Millimeter waves reflected by a possible target object are sent through the antenna feeds, the rat-race rings and ring mixers, for further signal processing. A portion of the energy of the Gunn oscillator is branched off by the ring mixer and mixed down. For further signal processing, each reception channel has a separate analyzer containing an amplifier, a low-pass filter, a downstream weighting filter and an A/D converter. The signals obtained after A/D conversion are analyzed using fast Fourier transform. An FMCW radar sensor designed accordingly has a range of approx. 150 meters and is preferably used in a vehicle for detection of one or more objects in a vehicle.
Such an FMCW radar sensor is also referred to below as an ACC (adaptive cruise control) radar sensor or simply an ACC sensor.
German Published Patent Application No. 197 24 496 discloses an obstacle detection device and a passenger safety device which utilizing the obstacle detection device. The obstacle detection device determines the distance between an obstacle and a vehicle by means of two distance measuring sensors, and it includes an impact angle calculating device, which calculates a plurality of positions of the obstacle by triangulation on the basis of the distance information provided by the two distance measuring sensors. Furthermore, the location of the obstacle, which is calculated by means of the plurality of calculated positions of the obstacle, is used to determine the impact angle formed by the obstacle and the vehicle. The two distance measuring sensors used are designed as radar sensors mounted on the right and left of the front part of a motor vehicle. The relevant distance measuring range of the sensors is in the range of less than a meter.
Such an obstacle detecting device is also referred to below as a precrash sensor or as a short-range radar.
U.S. Pat. No. 5,872,536 describes a multi-sensor object detection system which determines the instantaneous distance, relative velocity, collision angle and point of impact of a colliding object. This system has a plurality of signal transmitters which monitor a predetermined area within a certain angle range. Each signal transmitter emits a modulated carrier wave and receives the corresponding modulated carrier wave reflected by an object. The distance of the object from each individual signal transmitter is determined from the reflected signals on the basis of the amplitudes of the harmonic components of the reflected signal by using the Doppler effect. The instantaneous relative velocity relative to the object is determined on the basis of the frequencies of the harmonic components of the reflected signal. An impact detecting unit determines on the basis of the distance and relative velocity data whether there will be a collision, and if so, where the point of impact will be and at which angle the collision will occur.
A preferred embodiment provides for the use of two signal transmitters operating in a frequency range of 5.8 GHz. The maximum range of the sensor system is 3 meters, an especially sensitive range being up to approx. 1.5 meters. Such a sensor system is also referred to below as a precrash sensor or short-range radar.
German Published Patent 42 36 619 describes a distance determining device for automobiles which is equipped with an imaging and image recording system for imaging objects at a predetermined zone outside the automobile. This distance determining system is provided with a stereoscopic optical system and has a stereoscopic image processing device for processing the images produced by the optical system to calculate three-dimensional distance data. This system is capable of detecting a possible obstacle and the shape of the road in a distance range between 2 meters and 100 meters if the system is arranged in the upper area behind the windshield. The stereoscopic optical system includes cameras using solid-state imaging elements such as a CCD (charge coupled device). Thus, on the whole there are four CCD cameras in the system, two for observing short distances and two for observing long distances.
Such a distance determining device is also referred to below as a stereoscopic camera.
German Published Patent No. 42 09 536 describes an imaging cell for an image recording chip. A plurality of imaging cells is arranged in the form of a two-dimensional array. An analyzer logic circuit which is provided is designed for mapping high input signal dynamics on high output signal dynamics. The light-sensitive element of the imaging cell has two MOS transistors with which compression of the input signal dynamics and amplification of the output signal can be regulated. Such an image sensor can be used in the visible spectral range in particular.
Such an arrangement of imaging cells is also referred to below as a CMOS camera.
German Published Patent Application No. 41 10 132 describes a sensor system for automatic determination of the relative position between two objects. This sensor system has a combination of an angle-dependent sensor and an angle-independent sensor. The sensor which does not have angle resolution and is thus independent of angle is designed as a sensor that analyzes the distance from an object on the basis of a transit time measurement. Possible sensors include RADAR, LIDAR or ultrasonic sensors. The angle-dependent sensor has a geometric arrangement of optoelectronic transmitters and receivers arranged in the form of photoelectric barriers. The sensors, both of which cover a common detection zone, are arranged in close spatial proximity. To determine the relative position of an object, the distance from the object is determined by the angle-independent sensor, and the angle to the object is determined by the sensor having angle resolution. To determine a position relative to the object, the distance from the object is determined by the angle-independent sensor, and the angle to the object is determined by the sensor having angle resolution. The relative position is known on the basis of the distance from and the angle to the object. As an alternative to this arrangement of optoelectronic transmitters and receivers, the use of two sensors is proposed, which jointly determine the angle to the object by the triangulation principle.
German Published Patent Application No. 196 22 777 describes a vehicle distance controller which controls the throttle actuator of a vehicle, the brake actuator of the vehicle and an alarm device in the vehicle by a control unit. This control unit receives as input data the vehicle velocity and the data from two range locators and a tracking range locator. The two range locators are designed as optical range locators which emit light onto an object and detect the light reflected by the object. Types which operate according to the transit time or triangulation principle are provided. The two range locators are mounted on the two outer sides of the front of the vehicle and monitor the lane in front of the vehicle for vehicles cutting in from adjacent lanes. The tracking range locator has a pair of optical lenses arranged in parallel and image sensors arranged behind the respective lenses. The tracking range locator is used to observe another vehicle traveling in front in the same lane and select it for the vehicle distance control. If one of the two range locators detects a vehicle cutting into the lane during controlled operation, the alarm device is activated. This publication thus represents a combination of LIDAR sensors with a stereoscopic camera.
German Published Patent Application No. 195 18 978 describes an obstacle detection system for motor vehicles which can also determine the width and height of the obstacle in addition to its distance. The distance from an object in front of the motor vehicle and the width of the object are detected by a laser radar distance measuring unit. In the case of an optical imaging unit composed of a vertically mounted stereo video camera device, a suitable window is selected on the basis of the distance information supplied by the laser radar distance measuring unit. Knowing the previously determined distance information, it is possible as part of image analysis to determine the size and thus also the height of the object detected. For the case when an error occurs either in the laser radar distance measuring unit or in the stereo video camera unit, it is at least possible to still determine the information with regard to the distance from the object or obstacle. This publication thus presents a combination of a LIDAR sensor with a stereoscopic camera.
The object of the present invention is to provide an object detection system which is capable of accurately and reliably detecting objects in a detection zone that is as large as possible.
This object is achieved by the fact that the object detection system is made up of a combination of at least three object detectors, each having a different detection zone and/or a different detection range. This has the advantage that the optimum object detector Summary of the Invention. Objects can be detected especially reliably and accurately due to this measure.
In the case of an object detection system which is used in particular for a system for adaptive cruise control (ACC system) in a motor vehicle, it is advantageous that the detection zones lie mainly in the direction of travel in front of the motor vehicle, and that the detection zones overlap. It is especially advantageous if the maximum detection range of the object detector having the greatest detection range is at least about 100 meters, and if the detection range of the object detector having the smallest detection range begins at about less than one meter. It is also advantageous that the detection zone of the object detector having the greatest detection range has a detection width in at least portions of the detection zone which permits detection of objects in lanes adjacent to that of one""s own vehicle. With respect to the detection zone of the object detector having the smallest detection range, it is advantageous if it has a detection width corresponding at least to the width of one""s own vehicle. This ensures that the required detection width will be monitored in any detection zone.
It is especially advantageous that the object detectors operate according to at least two different technical concepts. Preferably at least one of the following is used as the technical concept:
1. Object detection based on acoustic signals, in particular ultrasound.
2. Object detection based on electromagnetic microwave radiation, in particular FMCW radar and/or pulsed radar.
3. Object detection based on image analysis, in particular a stereoscopic camera and/or a CMOS camera.
4. Object detection based on bundled light, in particular a LIDAR sensor.
In an embodiment of the present invention precisely three detection zones can be differentiated. In this case, an object detector based on electromagnetic microwave radiation is used in the first detection zone, while an object detector based on optical radiation and/or image analysis is used in the second detection zone. Then an object detector based on electromagnetic microwave radiation is used in the third detection zone. This specific object detector arrangement combines in a special manner the advantages of the individual types of object detectors. In the case of this arrangement, it is advantageous that the first object detector has a detection range of approx. 0.5 meter to approx. 7 meters. The second object detector has a detection range of approx. 2 meters to approx. 40 meters, and the third object detector has a detection range of more than approx. 40 meters. In the case of this arrangement, the first and second detection zones overlap by approx. 5 meters in an especially advantageous manner. The second and third detection zones also overlap. The resulting overlapping of the detection zones can be utilized so that the measured values originating from these zones can be used for separate analyses. These separate analyses may include, for example, joint tracking of the objects detected in the overlap zone and/or function monitoring of the object detectors and/or plausibility check of the measured data.
It is also advantageous that the object detectors are used for at least one additional application. This may be as a parking aid, for precrash detection, for start monitoring, to detect the condition or surface of the roadway, to recognize traffic signs, to recognize or determine the range of visibility, for adaptive light distribution, for headlight adjustment or for weather detection or as a rain sensor. This has the advantage that other additional sensors for these applications can be omitted.
It is advantageous to use the object detection system as part of a system for adaptive cruise control, the system being capable of continuously regulating the speed between standstill and the maximum speed of the motor vehicle. This adaptive cruise control, which has been expanded by adding this stop-and-go functionality, is an application of the object detection system according to the present invention.